as noted in my mail about the recent upload of nfs to backports [0], I believe the missing piece is:

printf '$portmap\trpcbind\n' > /etc/insserv.conf.d/rpcbind

That is missing indeed, even though (as suggested on the bug report you linked) it would maybe be more advisable to use a plus sign.

Could you report back if that works for you (or doesn't)?

Actually that was one attempt i made that couldn't solve the problem by itself.

The NFS sources don't get mounted directly by init (in which case that line would have worked), instead they are mounted by the post-up hook in ifupdown (see /etc/network/if-up.d/mountnfs), as i mentioned in my original mail.

That script belongs to "initscripts" (which, if my understanding is correct, would be very dangerous to "backport" once patched) and has a hardcoded check for /etc/init.d/portmap, so it has no knowledge of either insserv.conf nor rpcbind.

Sorry for the hassle on this; i'm not sure the best way to resolve the matter cleanly yet, but i'm open to suggestions.

I'm not really an expert on these matters, but since rpcbind can effectively replace portmap, it could be a solution to declare it as a portmap replacement in debian/control and make it provide the rpcbind -> portmap symlink on /etc/init.d to make things work.
It's not very clean but would allow not to touch the distribution's files too much.

Another solution could be to package the patched file and distribute a patched version of initscripts in the backports, but i don't know how hard to maintain that would be.